The present invention is in a process for the preparation of 2,5-dimethyl-2,5-dihydroperoxyhexane by the reaction of 2,5-dimethyl-1,5-hexadiene with hydrogen peroxide in an acidic medium.
2,5-Dimethyl-2,5-dihydroperoxyhexane (DHHP) is an important starting material for the preparation of cross-linking peroxides (dialkyl peroxides, such as e.g. 2,5-dimethyl-2,5-di-tert.-butylperoxyhexane, or perketals, such as 3,3,6,6,9,9-hexamethyl-1,2,4,5-tetraoxacyclonotane)(cf. GB-PS 936008), as well as of highly reactive bifunctional peresters.
In FR-PA 1291965 discloses the preparation of 2,5-dimethyl-2,5-di-tert.-butylperoxyhexane from 2,5-dimethyl-1,5-hexadiene by reaction with tert.-butylhydroperoxide. However, the yield of 26% thereby obtained is very unsatisfactory and, furthermore, according to this process, only dialkylperoxides but no perketal or perester derivatives of DHHP are obtained.
From the prior art, a process for the preparation of 2,5-dimethyl-2,5dihydroperoxyhexane (DHHP), from 2,5-dimethylhexane with oxygen is known.
EP-A-0513711 describes a process for the preparation of aliphatic hydroperoxides, e.g. of 2,5-dimethyl-2,5dihydroperoxyhexane (DHHP), by the reaction of a corresponding tetrahydrofurane derivative with hydrogen peroxide.
U.S. Pat. No. 4,154,768 describes a general process for the preparation of tert.-alkylhydroperoxides from asymmetric secondary olefins by reaction with hydrogen peroxide in a reaction mixture containing a strong acid.
According to JP-A-3215468 and JP-A-3190856, hydroperoxides are obtained by the reaction of an olefin or alcohol with hydrogen peroxide in the presence of a strong acid.
Usually, the preparation of 2,5-dimethyl-2,5dihydroperoxyhexane (DHHP) takes place by the reaction of 2,5-dimethylhexane-2,5-diol with hydrogen peroxide in the presence of an acidic catalyst, in general using sulphuric acid (cf. Rust, J. Am. Chem. Soc. 79 (1957) 4000, 4002; L. Criegee, Erdol und Kohle, 15 (1962) 523, 524, 528; Criegee and Paulig, Chem. Ber., 88 (1955), 712, 716; Criegee and Dietrich, Liebigs Ann. Chem. 560 (1948) 141; L. Dulog and A. Sanner, Tetrahedron Letters, 51 (1966) 6353-6358). According to these processes, the dosing of the diol takes place as a solid, which is a disadvantage. Another disadvantage of this process is the easy formation of cyclisation products (e.g. 2,2,5,5-tetramethyltetrahydrofuran) from the diol under the influence of acids which gives poor yields of dihydroperoxide and a contaminated product.
Therefore, there was still a great need for a process for the preparation of 2,5-dimethyl-2,5-dihydroperoxyhexane (DHHP) which can be carried out in a simple and technically advantageous way, and by which the DHHP is obtainable in high yield.
This problem has been solved by the process of the present invention.